Welch
motor with gyrating rotor

ABSTRACT

(THIS DISCLOSURE RELATES TO A NEW TYPE OF) A STEPPER MOTOR (WHEREIN THERE IS PROVIDED) HAVING A STATOR WITH A ROTOR ECCENTRICALLY POSITIONED IN THE STATOR FOR ROLLING MOVEMENT ABOUT THE INTERIOR OF THE STATOR SUCH THAT THE AXIS OF THE ROTOR REVOLVES ABOUT THE AXIS OF THE STATOR IN ONE DIRECTION. AN OUTPUT SHAFT IS PROVIDED WITH AN OUTPUT RING PREFERABLY HAVING GEAR TEETH AND CONCENTRICALLY POSITIONED WITHIN THE STATOR WITH ITS PERIPHERY IN ENGAGEMENT WITH THE PERIPHERY OF THE GYRATING ROTOR. THE DIAMETER OF THE ROTOR IS INTERMEDIATE THE INSIDE DIAMETER OF THE STATOR AND THE DIAMTER OF THE OUTPUT SHAFT RING SO THAT THE OUTOUT SHAFT RING WILL ENGAGE AN INSIDE SURFACE OF THE ROTOR AND WILL BE CAUSED TO ROTATE UPON GYRATING MOVEMENT OF THE ROTOR. THE ROTOR ITSELF IS MAINTAINED IN ROLLING ENGAGEMENT WITH THE INTERIOR OF THE STATOR BY THE MAGNETIC ATTRACTION OR REPULSION PRODUCED BY SUITABLE STATOR FIELD WINDINGS AND POLE PIECES WHICH WOULD FUNCTION TO PROVIDE A ROTATING MAGNETIC FIELD IN THE MANNER SIMILAR TO CONVENTIONAL STEPPER MOTOR STATOR FIELDS. GEAR TEETH MAY BE PROVIDED BETWEEN THE ENGAGED ROLLING PORTIONS TO PREVENT SLIPPGE. THE RELATIVE DIAMETERS OF THE STATOR, ROTOR, AND OUTPUT SHAFT RING AND ADJUSTED TO PROVIDE A DESIRED INCREMENTAL STEP OR SHAFT ROTATION FOR A GIVEN DEGREE OF ROTATION OF THE STATOR FIELD.

Aug. 1, 1972 HE. c. WELCH I MOTOR WITH GYRATING ROTOR Original FiledOct. 21, 1966 2 Sheets-Sheet 1 I5 A U I8 IO m STEP CON- T ROLLERINVENTOR.

+ /F3 I BY ELVIN C.WELCHI ATTORNEYS 1, 1972 E. c. WELCH Re. 27,446

MOTOR WITH GYRATING ROTOR Original Filed Oct. 21, 1966 2 Sheets-Sheet 226 \W A ga g I INVENTOR.

ELVIN C. WELCH ATTORNE.

United States Patent 27,446 MOTOR WITH GYRATING ROTOR Elvin C. Welch,9905 W. J etferson Blvd., Culver City, Calif. 90230 Original No.3,452,227, dated June 24, 1969, Ser. No. 588,497, Oct. 21, 1966.Application for reissue June 7, 1971, Ser. No. 150,493

Int. Cl. H02k 37/00 U.S. Cl. 310-49 Claims Matter enclosed in heavybrackets I: II appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE [This disclosure relates to a new type of] Astepper motor [wherein there is provided] having a stator with a rotoreccentrically positioned in the stator for rolling movement about theinterior of the stator such that the axis of the rotor revolves aboutthe axis of the stator in one direction. An output shaft is providedwith an output ring preferably having gear teeth and concentricallypositioned within the stator with its periphery in engagement with theperiphery of the gyrating rotor. The diameter of the rotor isintermediate the inside diameter of the stator and the diameter of theoutput shaft ring so that the output shaft ring will engage an insidesurface of the rotor and will be caused to rotate upon gyrating movementof the rotor. The rotor itself is maintained in rolling engagement withthe interior of the stator by the magnetic attraction or repulsionproduced by suitable stator field windings and pole pieces which wouldfunction to provide a rotating magnetic field in the manner similar toconventional stepper motor stator fields. Gear teeth may be providedbetween the engaged rolling portions to prevent slippage. The relativediameters of the stator, rotor, and output shaft ring are adjusted toprovide a desired incremental step or shaft rotation for a given degreeof rotation of the stator field.

This invention relates generally to motors and more particularly to animproved motor incorporating a gyrating rotor.

While the principles of the invention are applicable to many types ofmotors including hydraulic as well as electrical motors, the preferredembodiment of the invention will be described with respect to anelectric stepper motor wherein the novel features of the invention areparticularly advantageous.

Conventional stepper motors include a stator structure incorporatingsuitable field windings for providing a magnetic field vector which maybe caused to move successively to various circumferential spatialpositions by proper sequential energization of the stator windings. Byemploying a rotor of magnetic material, the rotor will follow themagnetic field and thus move a discrete step for each step of the fieldvector. A suitable controlling means in the form of a logic circuitresponsive to input pulses may be provided to effect the desiredsequential energization of the stator field windings and thus cause astepping of the rotor about its axis of rotation in accord with theinput pulses received.

One of the major concerns of stepper motors of the foregoing typeinvolves the moment of inertia of the rotor itself. In starting from onestepped position to the next stepped position, and in stopping in thenext stepped position, the rotor inertia can interfere with accuratestepping movement, particularly when the stepping takes place at a highrate of speed. This inertia can cause the rotor to either fail toaccomplish a stepped position or to overshoot or actually skip steppedpositions. It the output shaft of the rotor operates in conjunction withother computer equipment where it is desired that the number of stepsare exactly equal to a number of pulses, the entire computer can recordfalse information if the rotor should miss or skip any particular stepprovided for in the input information.

Another important consideration is the desirability, in certainapplications, of providing a stepper motor in which the output shaftangle rotation provided for each step can be readily adjusted, such asto a fairly small angle even though the field executes steps. A smalloutput shaft angle can be accomplished by providing several statorwindings circumferentially distributed about the rotor and arranged togenerate a magnetic field vector which steps through the desired smallangle so that the rotor and its shaft will similarly step through thesmall angle. However, such an arrangement is low in efiicicncy sinceonly a small fraction of the total windings available can be used at onetime. There is also involved increased expense in providing thenecessary number of windings. Further, the controller for interpretinginput pulses to provide the desired stepping of the vector field isincreased in complexity. An alternative method would be to provide asimple mechanical reduction gearing between the rotor and a suitableoutput shaft which would reduce the rotation of the output shaft to thedesired small shaft angle step. This latter solution, however, increasesthe overall inertia of the device as a consequence of the reductiongears involved and also adds to the general bulk and expense of thestepper motor.

A third most important consideration in stepper motors in connectionwith the foregoing is the desirability of being able to effect anextremely large number of steps per unit time for a given stator fieldwinding configuration and controller. For example, if a field windingstator configuration is such that the generated magnetic field vector iscaused to spatially execute 90 steps, the rotor in the conventional typestepper motor will similarly execute 90 steps. If the desired number ofsteps per unit time is large, such as of the order of 4000 steps persecond, it would be very diflicult to rotatably mount the rotor for thisrate of speed. And even if such could be accomplished, the rotorbearings would quickly wear out. It would be desirable to enable theoutput shaft to execute steps at an extremely rapid rate withoutrequiring that the rotor and other components move at such high speedsand without having to make any changes in the magnetic field generatingequipment or windings, all to the end that long life is assured and highmagnetic efficiency is preserved.

With the foregoing considerations in mind, it is a primary object ofthis inventon to provide an improved motor which may be operated as astepper motor wherein the foregoing problems inherent in present steppermotors are overcome.

More particularly, it is an object to provide an electric stepper motorwherein the inertia of the movement of the rotor is substantiallyreduced as compared to the inertia experienced by the rotors ofpresently available stepper motors all to the end that the stepper motoroutput shaft rotation can be stepped at an extremely rapid rate withnegligible possibility of mis-stepsas a consequence of high inertia.

Another important object is to provide an improved electric steppermotor in which the steping angle of the output shaft may be easilyadjusted without having to alter a basic stator winding configurationand stator winding energy input for generating a magnetic field vector,or without the necessity of complicated gear reduction systems of thetype that would normally be necessary if employed with conventional typestepper motors.

Another important object is to provide an improved electric steppermotor in which the actual steps of an output shaft may be effected at anextremely rapid rate without undue wear on bearings or other componentsof the system.

Still other objects of this invention are to provide an improvedelectric stepper motor is relatively economical to manufacture, longlived, is not bulky, and does not require expensive components and thelike for realizing extremely accurate stepping action.

Briefly, these and many other objects and advantages of this inventionare attained by providing a stator with a rotor eccentrically positionedin the stator for rolling or orbiting movement about the interior of thestator such that the axis of the rotor [revolves] orbits about the axisof the stator in one direction. The rotor itself, as a consequence ofthe rolling action about the inside of the stator, is caused to rotateabout its own axis in an opposite direction. As a consequence of thesecontrary directions, the net moment of inertia of movement of the rotorto successive spatial positions about the interior surface of the statoris reduced substantially relative to the moment of inertia of the rotorif it were concentrically mounted in the stator for rotation.

The motor structure also contemplates the provision of an output shaftincluding an output ring preferably having gear teeth and concentricallypositioned within the stator 'with its periphery in engagement with theperiphery of the gyrating rotor. In the preferred embodiment, thediameter of the rotor is intermediate the inside diameter of the statorand the diameter of the output shaft ring so that the output shaft ringwill engage an inside surface of the rotor and will be caused to rotateupon gyrating movement of the rotor. The rotor may be a hollowcylindrical sleeve over its complete length, or may be a solid cylinderexcept for shallow cup shaped indentations at each end which willprovide the required inside surface. The rotor material may be eitherpolarized magnetic material such as alnico, or non-polarized such assoft iron.

The rotor itself is not structurally constrained in radial directionswithin the stator interior bore but rather is maintained in rollingengagement with the interior of the stator by the magnetic attraction orrepulsion produced by suitable stator field windings and pole pieceswhich function to provide a rotating magnetic field in a manner similarto conventional stepper motor stator fields. Slippage between therolling surfaces may be prevented if desired by providing gear teeth onportions of the surfaces in actual contact. Either an odd or even numberof stator poles may be employed with one or more poles excitedsimultaneously. By adjusting the relative diameters of the stator,rotor, and output shaft ring, a desired incremental step or shaftrotation can be provided for a given degree of rotation of the statorfield. In this respect, the same arrangement of stator, rotor, andoutput shaft ring which functions to reduce substantially the moment ofinertia of the rotor movement also functions as a gear reduction so thatdesired small angle steps of an output shaft can be achieved and anextremely rapid stepping rate can be achieved without undulycomplicating the overall motor structure itself and 'without materiallyaltering the desired low moment of inertia.

A better understanding of the invention will be had by now referring tothe accompanying drawings in which:

FIGURE 1 is a schematic perspective view illustrating a stator, rotor,output shaft, and other basic components making up an electric motor inaccord with one embodiment of this invention;

FIGURE 2 is a front elevational schematic view of the motor of FIGURE 1illustrating the rotor and output shafts in first positions relative tothe stator;

FIGURES 3, 4, and 5 are views similar to FIGURE 2 but illustrating therotor and output shaft in successive positions during a steppingoperation of the motor;

FIGURE 6 is a cross section of an actual embodiment of the structureillustrated schematically in FIGURE 1; and

FIGURE 7 is a front schematic view of a modified embodiment of theinvention.

Referring first to FIGURE 1 there is illustrated a stator structure 10,which in the example chosen for illustrative purposes, is the shape of acylindrical body. Secured to the stator are suitable stator windingstructures including pole pieces 11, 12, 13 and 14 spatially positionedsuccessively at Each of the pole pieces includes windings having inputconductors designated at 15, 16, 17, and 18, respectively. These inputconductors connect to a step controller indicated schematically by thebox 19.

The step controller may include suitable logic circuits responsive to aseries of input pulses applied to clockwise and counterclockwiseterminals which will effect a sequential stepping of the magnetic fieldabout the rotor in a clockwise or counterclockwise direction. As asimple illustration, if the windings for the pole pieces 11, 12, 13, and14 are sequentially energized one at a time, there will result amagnetic field vector which will assume successive spatial positionsseparated by 90 about the stator axis in a clockwise direction whenviewed from the left end of FIGURE 1. If the various pole piece windingsare energized in an opposite sequence such as 11, 14, 13, and 12, themagnetic field vector will be caused to rotate in 90 steps in anopposite direction about the stator.

Disposed within the stator structure 10 is a cylindrical rotor 20 madeof magnetic material such that it Will be attracted to the interiorstator wall by the particular field pole piece whose winding isenergized. This rotor structure defines in part a rotor ring which mayconstitute the actual portion engaging the interior bore of the stator10.

In the preferred embodiment of the invention, the rotor constitutes apermanent magnet of given polaribation and diametrically opposite polepieces are energized in an opposite sense simultaneously to increase themagnetic field. Thus, pole pieces 11 would exert an attractive force andpole piece 13 would simultaneously exert a repelling force. In the nextstep, pole piece 12 would exert an attractive force and pole piece 14would simultaneously exert a repelling force. By this type of sequentialenergization, the magnetic efficiency is increased since one-half of thetotal windings are utilized rather than one-fourth.

Suitable controller circuits responsive to clockwise andcounterclockwise input pulses for effecting the stepping of a magneticfield vector are illustrated in detail in my United States Patent No.3,239,738.

At the front of the rotor 20 there is provided an output shaft structure21 mounted along the axis AA of the stator 10. This output shaft ismounted for rotation about this axis by suitable bearings such asindicated at 22. Actually, bearings are provided at both ends as willbecome clearer when an actual embodiment is described as opposed to theschematic showing in FIGURE 1.

It will be noted in FIGURE 1 that the interior wall of the stator 10includes gear teeth 23 and for convenience interminology, thecylindrical structure of the stator upon which the gear teeth are formedwill be designated a stator ring. Similarly, the rotor 20 includesexterior gear teeth 24 and interior gear teeth 25 on a portion of therotor which will hereafter be referred to as a rotor ring. Finally, theoutput shaft structure 21 includes an enlarged diameter portion uponwhich outer gear teeth 26 are provided and this portion supporting thegear teeth 26 will be referred to as an output ring.

The diameters of the stator ring, rotor ring, and output ring are suchthat the gear teeth 23 on the inside stator ring are in meshingengagement with the gear teeth 24 on the exterior of the rotor when theinterior gear teeth 25 are in engagement with the exterior gear teeth 26on the output shaft, the output shaft itself being maintained in aconcentric or coaxial relationship with the axis AA of the stator bore.

Referring now to FIGURES 2, 3, 4, and 5, the operation of the structuredescribed in FIGURE 1 will be understood. Assume first that the stepcontroller 19 of FIGURE 1 receives a series of clockwise input pulsesand functions through its logic circuit to sequentially energize thevarious field windings in a clockwise direction. The successive spatialpositions of the stator field vector are indicated schematically inFIGURES 2, 3, 4, and 5 by the vectors F1, F2, F3, and F4, respectively.

When the stator field is as represented by the vector F1, the rotor 20will be in the position illustrated in FIGURE 2. For convenience inindicating the relative rotational positions of the rotor and the outputshaft ring, the solid arrows R and are drawn as shown. When the upperstator field winding is de-energized and the next successive fieldwinding energized, the vector F1 is removed and the vector F2illustrated in FIGURE 3 is generated. The rotor is thus magneticallyattracted to the position illustrated in FIGURE 3 and this motion iseffected by means of the rotor rolling about the interior arcuate wallof the stator 10 to the position shown in FIGURE 3. This rolling actionof the rotor results in a rotation of the rotor about its own axis acertain number of degrees in a counterclockwise direction as viewed inFIGURES 2 and 3. Thus, the arrow R will assume the position illustratedin FIGURE 3 which is in a counterclockwise direction relative to itsposition in FIGURE 2. On the other hand, the axis of the rotor itselfhas revolved 90 about the axis of the stator as will also be evidentfrom FIGURE 3. The output shaft ring 21 will also be rotated as a resultof the rotation of the rotor so that the arrow will be repositioned asshown.

The next stepping of the stator field will result in the vector F3 beinggenerated as illustrated in FIGURE 4 and this magnetic field will thencause the rotor 20 to roll to the position illustrated in FIGURE 4. Thisrolling action of the rotor will again result in a rotation of the rotorabout its own axis in a counterclockwise direction while the geometricalcenter of the rotor itself revolves 90 about the center axis of thestator. Also the output shaft will be rotated to a new position as shownby the arrow 0.

FIGURE 5 shows the next successive position of the rotor and outputshaft upon energization of the field F4.

When the field F4 is de-energized and the field vector F1 again applied,the rotor will then be back into the position illustrated in FIGURE 2insofar as its own axis is concerned. That is, when back in the positionillustrated in FIGURE 2, the rotor axis has made one complete revolutionabout the center axis of the stator. However, the arrow R will now be inthe position R indicated in dotted lines in FIGURE 2 and the arrow 0 onthe output shaft will be in the position of the dotted line arrow 0' inFIG- URE 2.

If the inside diameter of the stator is indicated D1 as shown in FIGURE2, the outside diameter of the rotor D2, the inside diameter of therotor D3, and the outside diameter of the shaft ring D4, the followingrelationships exist: The degree of rotation of the rotor about its ownaxis during revolving movement of its axis about the center axis of thestator, is given by:

where 6 equals the angle of rotation of the rotor 20 about its own axis;that is, the angle through which the arrow R moves from FIGURE 2 toFIGURE 3; and

0 equals the angular movement of the field vector F1 to the position F2which corresponds to the angular movement of the axis of the rotor aboutthe axis of the stator.

Also,

where 0 equals the angle through which the output shaft 21 rotates.

By way of example, if the ratio of Dl/D2 is fourthirds and the ratio ofD3/D4 is five-fourths, then the output shaft angle 0 is given by Thus, 0will always equal two-thirds of the angle 9 through which the fieldvector has moved which, as stated, equals the angle through which theaxis of the rotor has revolved about the center of the stator. Theresulting negative sign simply indicates that the rotation of the outputshaft is opposite in sense to the rotation of the field vector.

In the schematic drawings illustrated in FIGURES 2, 3, 4, and 5, theabove proposed ratios of diameters are substantially depicted. The arrow0 has thus rotated towards 240 as indicated by the dotted line 0 and thearrow R has rotated 120 in an opposite direction as indicated by thedashed line R in FIGURE 1.

It will be appreciated from the above, that if the outside rotordiameter D2 is equal to the inside stator diameter D1 there will be norotational movement of the rotor since the rotor axis will besubstantially coincident with the stator axis. However, if the rotordiameter D2 is slightly less than the inside stator diameter D1, therewill be a very slight rotational movement of the rotor as the same rollsabout the interior of the stator. This angular movement will beextremely small and as a result, the angular movement of the outputring, whose diameter would now be very close to the diameter D3 of theinterior of the rotor would be correspondingly small. Further, it willbe evident that by making the diameters close to each other as describedthere is actually very little movement of the rotor in its gyratingaction and thus the execution of the steps by the rotor can be effectedextremely rapidly with substantially no inertia problems.

With respect to the foregoing, the decreased inertia is a consequence ofrotation of the rotor in an opposite sense to the motion of gyration.This action results in a subtraction of the moment of inertia of onefrom that of the other. Thus, if M represents the mass of the gyratingrotor, then the net moment of inertia I is given by:

D1 D2 2 I 3/2M It can be seen from the above equation that as D2approaches D1, the net moment of inertia approaches zero.

Moreover, it will be appreciated that the shaft angle executed for eachstep or spatial repositioning of the field through may be adjusted toany desired value in accord with Equation 2 by appropriately selectingthe proper diameters for the stator, and inside and outside of the rotorring.

The provision of the gear teeth assures a positive drive between thevarious engaging rings. Since the number of gear teeth on each ring isdirectly proportional to the diameter of the ring, the number of gearteeth may be substituted for the various diameters, respectively, andthe above relationships will still be accurate.

As a speecific example of an actual embodiment of the invention, theremay be provided 75 gear teeth on the inside of the stator, asrepresented by the gear teeth 23 in FLIGURE l, and 72 gear teeth on theexternal portion of the rotor. Under these conditions, as the rotorrolls through one complete gyration so that its axis revolves 360 aboutthe stator axis, the rotor comes up three teeth short of its originalposition.

Therefore, from Equation 1, bearing in mind that the diameters areproportioned to the number of teeth, the angle is given by:

If it is assumed that the number of teeth on the inside of the rotorring as indicated at 25 in FIGURE 1 is 48 teeth and the number of teethon the outside of the shaft output ring as indicated at 26 is 45 teeth,then the angle through which the output shaft moves will be given FIGURE6 illustrates in cross section a closer representation to the actualstructure of the motor schematically depicted in FIGURE 1. In FIGURE 6,the components corresponding to FIGURE 1 have been provided with thesame numerals. It will be noted that the stator housing structure 10includes front and rear end caps 27 and 28. The front end cap serves tosupport the front bearings 22. In addition, the output shaft 21 andcorresponding rotor gear ring 26 include a simple thrust ball bearing 29bearing against the left end of the rotor 20.

A similar bearing structure is incorporated in the end cap 28 for theright hand end of the rotor structure wherein there is provided asimilar ball bearing 30 for a shaft 31 carrying a similar gear ring forcooperation with inside gear teeth on the opposite end of the rotor. Asshown, bearings corresponding to the bearings 22, are provided at 32 inthe end cap 28. Essentially, the shaft 31 is simply an idler shaft butserves to stabilize the rotor structure in its gyrating action.

In the embodiment depicted in FIGURE 6', the rotor 20 constitutes apermanent magnet, preferably of alnico, and is shown in its up positionwherein the pole piece 11 is energized to attract the magnetic rotor 20and, as described heretofore, the opposite pole piece 13 is energized torepel the magnet 20 simultaneously. A particular advantage in employinga permanent magnet rotor resides in the provision of a desirable dampingaction thereby lessening any over-shoot effect of the rotor while in itsmotion. This damping results from the magnetic flux lines of the rotormagnet cutting the stator windings and producing a voltage in the statorwindings which is opposite in sense to the voltage applied by thewinding leads thereby providing a breaking or damping action on therotor motion.

FIGURE 7 is a partially schematic front cross-sectional view of amodified motor wherein a stator housing 33 incorporates only threestator pole pieces 34, 35 and 36. A suitable gyrating rotor structurewhich may be in the form of a sleeve 37 provided with suitable gearteeth cooperates with an output gear ring structure 38 in the samemanner as described with respect to the embodiment of FIGURE 1. In theembodiment of FIG- URE 7, the three field windings may be sequentiallyenergized to result in the axis of the rotor gyrating through 120 steps.In this embodiment, only one-third of the stator magnetic circuit isenergized at any one time and in this respect, the magnetic efficiencyis not as great as in the case of the four pole pieces provided in thestator field wherein diametrically opposite poles may be energizedsimultaneously in an opposite sense. However, FIGURE 7 represents theminimum number of stator pole pieces necessary to avoid any ambiguitiesin elfecting a stepper action for the gyrating type motor underconsideration.

The fundamental considerations in providing a stepper motor with threeor many more stator pole pieces in accord with the present invention,are: First, the rotor must be isotropic about its own axis such thatrotations about its own axis does not alter the forces or torquesproduced by the action of the stator on the rotor. In other Words, itmust be dynamically and electrically symmetrical about its own axis.Second, the rotor must be anisotropic for rotation of its axis about thestator axis. The stator may then utilize this anisotropic property toproduce a torque or force on the rotor which is a function of theangular position of the rotor axis with respect to the stator.

From the foregoing description, it will thus be seen that there isprovided a greatly improved motor structure particularly well suited forstepper operation wherein all of the objects set forth are fullyrealized.

Various changes that fall within the scope and spirit of this inventionwill occur to those skilled in the art. The motor is therefore not to bethought of as limited to the specific embodiments set forth merely forillustrative purposes.

What is claimed is:

1. An electric motor including, in combination: a stator means having aninterior bore; a rotor means of magnetic material within said statormeans interior bore means and eccentrically positioned for rollingmotion about the interior bore of said stator means the axis of saidrotor being parallel to and revolving about the center axis of saidstator means said rotor means being structurally unconstrained in radialdirections within said stator means interior bore; output means coupledto said rotor means for providing an output rotation constituting afunction of the rotation of said rotor means about its own axis as aconsequence of its rolling action about the interior bore of said statormeans said roller means being isotropic about its own axis; and magneticfield generating means for generating a magnetic field flux path in thedirection of the axis of said rotor means in a manner to assumesuccessive spatial positions about said stator means with time wherebysaid rotor means is caused to roll about the interior of said statormeans by said magnetic field, the direction of rotation of said rotormeans being opposite to the direction of revolving of said axis of saidrotor means about said center axis whereby the net moment of inertia ofsaid rotor means is reduced substantially relative to the moment ofinertia of said rotor means if concentrically mounted in said statormeans for rotation.

2. A motor according to claim 1, in which said magnetic field generatingmeans includes stator winding means circumferentially spatiallypositioned about said stator means; and a controller connected to saidwinding means for energizing the same in a given sequence to step saidfield through said successive spatial positions in response to inputpulses whereby a stepper motor is provided.

3. A motor comprising:

a stator means;

a rotor means disposed within said stator for orbiting about the statoraxis within the interior of said stator means;

means for generating a force which acts on said rotor means to cause itto orbit about the axis of said stator within the interior of saidstator means;

means maintaining said rotor means in engagement with said stator meansinterior as it orbits about the axis of said stator means;

output means to provide an output rotation in response to said rotororbiting movement.

4. The motor of claim 3 wherein said means maintaining said rotor meansin engagement with said sator means interior as it orbits about the axisof said sator means includes means creating force vectors acting on saidrotor means to maintain said engagement throughout said orbitingmovement.

5. The motor of claim 4 wherein said means creating force vectors causessaid force vectors to shift about the axis of said stator means as saidrotor means orbits.

6. The motor of claim 3 wherein said means creating said force vectorsincludes means creating a magnetic attraction vector between said rotormeans and said stator means.

7. The motor of claim 6 wherein said means for creat- 5 ing a magneticattraction vector also provides said force generated by said meanscausing said rotor to orbit about said stator means axis.

8. The motor of claim 7 further including means causing the line ofaction of said magnetic attraction vector to assume successive positionsabout the stator means axis as said rotor means orbits.

9. The motor of claim 3 wherein said output means includes an outputgear concentric with said stator means and meshing said gear teethformed on a position of said rotor means.

10. The motor of claim 3 wherein said means maintaining said rotor inengagement with: said stator includes a rotor configuration whereinportions thereof are permanently magnetized.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,322,984 5/1967 Anderson 310-82 2,857,536 10/1958Light 310-82 3,334,253 8/1967 Hill 310-82 2,761,107 8/1956 Giertz 310-822,561,890 7/1951 Stoddard 310--82 2,761.079 8/1956 Hedstrom 310663,147,425 9/1964 Christoff 310--82 3,262,081 7/ 1966 Fairbanks 310--823,308,320 3/1967 Spencer 31082 J D MILLER, Primary Examiner R. SKUDY,Assistant Examiner US. Cl. X.R.

